Apparently many do have a problem with it, as the Christian faith is currently under assault. The supreme law of the land is the constitution. The 1st amendment in that constitution prohibits government from prohibiting the free exercise of religion. That is what's currently happening.
Our laws ARE already based on Christianity. What do you think the Declaration of Independence means when it says " These inalienable rights, granted by our creator " ?
There is no such thing as " Christian morality " Just objective morality. Gay marriage is by definition, perverted, immoral, and destructive behavior. Not according to Christianity, but according to reality and science.
Christians have no problem with adult-stem cell research, which has demonstrated much scientific progress. We however do have a problem with embryonic stem-cell research which has shown zero promise. And has produced nothing more than Dr. Frankenstein freak experiments which liberals try to use to justify murdering unborn babies.